1. Technical Field
The present invention relates to power supplies in general, and in particular to power supplies having multiple switching regulators. Still more particularly, the present invention relates to an apparatus for controlling voltage sequencing for a power supply having multiple switching regulators.
2. Description of the Related Art
In most electronic designs, a circuit board is populated with a number of electronic circuit devices, each of which may be powered by a single voltage source, such as a power supply having a positive voltage potential referenced to a ground voltage potential. Generally speaking, the electronic circuit devices receive power from the voltage source that is turned on and off in accordance with the requisite usage for the electronic circuit devices. In practice, it is often necessary to condition the input voltage from the power supply to be received at the electronic circuit devices in order to ensure the proper functioning of the electronic circuit devices.
Electronic circuit devices having multiple supply voltages are typically sensitive to voltage sequencing. Hence, problems associated with a typical electronic design usually arise when there is a need to sequence the electrical power supplied to a number of electronic circuit devices during power transitions. For example, the power supply AD588, manufactured by Analog Device, Inc., is a highly accurate voltage reference that requires +15 volt and −5 volt to generate a 10 volt reference voltage for precision circuitry. If during a power-out (ie., +V1 and −V2 are energized), the +15 volt is up before the −5 volt, the +10 volt reference may move to +13 volt. Likewise, if the −5 volt comes up before the +15 volt, the +10 volt reference may move to −2 volt.
Depending on the application and the circuit configuration, the shifting of reference voltage can cause very undesirable results such as loss of control, latch-up, etc. Consequently, it is desirable to provide an apparatus for controlling voltage sequencing for a power supply having multiple switching regulators such that reference voltage shifting can be avoided.